Vibrational assessment of the stability of root keeper in magnetic attachment system

Recently, a magnetic assembly prosthesis (root keeper @ ) has been increasingly used in treating partial edentulous patients. However, interfacial problems between the cement and Root Keeper have not been systematically discussed. To assess the stability problems of Root Keeper, numerical simulations were performed in this study. A 3-D finite element model of the Root Keeper-cement-dentin system was established for modal analysis. To monitor the change in resonance frequency (RF) values when root keeper began to loosen, contact spring elements were adopted to simulate the interface conditions between Root Keeper and the cement. The model was first validated against a series of modal testing experiments. Then, RF values of the first vibration mode of the model with various boundary conditions were calculated and compared. Our in vitro results showed that the measured RF values changed significantly (p<0.01) under various surrounding material conditions. Results obtained from finite element (FE) simulations demonstrated that root keeper would fully loosen when the constant values of the spring elements were lower than 107. Furthermore, the RF values of the model increased significantly (p<0.01) when the constant was increased from 107 (6.16 kHz) to 1010 (15.52 kHz), and then reached a plateau. These results demonstrate that the resonance frequency has the potential to be used as a parameter for monitoring the stability of root keeper.